With time on his hands, the former “Tonight Show” host set up a Twitter account and declared last week that he’d follow just one person on the site.

“I’ve decided to follow someone at random. She likes peanut butter and gummy dinosaurs. Sarah Killen, your life is about to change,” O’Brien tweeted.

“It’s been amazing. It really has changed my life completely,” said Killen, an engaged 19-year-old from Fowlerville, Mich.

By late yesterday, she had amassed 17,000 followers — along with a plethora of wedding gifts and thousands in donations to a charity given by Conan’s more than 590,000 Twitter followers for her Sept. 25 wedding.

After Conan became a Killen devotee, Florida retailer Hornblower’s sent her a new Apple computer. Then New York dress company Kelima K offered to make the blushing bride-to-be a custom-made gown.

More importantly, Killen said, the Conan connection has helped her raise more than $2,500 in pledges for a three-day breast-cancer charity walk in August. J